Doppler distortion in fullrange drivers

[sharpi31]

It seems that a common perceived shortcoming of fullrange drivers is doppler distortion. The more I think about this, the more the common explanations worry me...

Please tell me where my logic fails:

Assume the situation where a single full range microphone is used to record a live performance. The microphone capsule will move back and forward under the influence of lower frequencies, while simultaneously moving under the influence of higher frequencies.

As the driver moves forward under the influence of a bass signal, higher frequencies will be artificially raised as the recording membrane is moving towards the signal source over time. Similarly, higher frequencies will be artificially lowered as the membrane moves away from the signal source over time.

So if we play this recording back using a fullrange driver in correct phase, doppler distortion will kick in. As the driver moves forward under the influence of bass, it will again raise higher frequencies artificially as the source moves towards the listener over time. Note that these frequencies have already been raised during the recording process described above.

But what happens if we run the fullrange driver out of phase with the microphone? The doppler distortion on the recording is cancelled out. The raising of high frequencies caused by the membrane moving toward the signal source during recording is undone when the loudspeaker moves away from the listener during playback!

The main point being, if a single capsule is used for recording mixed frequency audio; a single driver out of phase can reproduce the full audio range without doppler distortion.

C'mon: beat me down if my hypothesis is wrong!

[phase_accurate]

Due to the smallish excursions of mic diaphragms Doppler distortion is a non-issue on the recording side.

It is however an issue on the reproduction side. Martin Colloms claims that it is an issue with fullrangers for excursions >3mm peak IIRC.

Your thesis has ben raised on this forum at least once so far.

Regards

Charles

Edit: Your thesis could be valid to a certain degree if both - the mic and the speaker - have exactly the same excursion, which is almost impossible to achieve.

[Hartono]

"a single driver out of phase can reproduce the full audio range without doppler distortion"

Beat beat beat beat beat beat


if doppler distortion is really significant in loudspeaker
above approach is downright wrong.

[Hartono]

ok where your logic fail is :

different size full range behave differently ( larger one have less excursion for same spl ).

[sharpi31]

Thanks phase-accurate,

I understand that the excursion of the capsule and driver would need to be identical for complete 'doppler distortion cancellation'.

The main point is that the combination of single capsule and single driver seems to be the best mechanism for avoiding doppler distortions. Most of the information available suggests that single drivers are more prone to this type of distortion, which is simply misleading.

Once you open up the discussion to considering how doppler effects are captured during recording, I would propose that the single driver is at worst still better than any 2, 3 or 4 way system.

Unless of course you have a system where you have multi-way microphone capsules mirroring the excursion of the drivers in multi-way speakers, which would seem even more difficult to achieve!

In the real world every disc is recorded differently using different numbers of different mics. No speaker system can ever account for these differences, so the minimalist in me says KISS :-)

[phase_accurate]

Once you open up the discussion to considering how doppler effects are captured during recording, I would propose that the single driver is at worst still better than any 2, 3 or 4 way system.

Quite the contrary is the case. Full-range drivers are always worse in this respect than multiway systems.
Maybe I wasn't clear enough: With the veeeeeeery small excursions of a mic diaphragm Doppler distortion will be negligible. Your fullranger will therefore not compensate for anything that isn't there in the first place. It will also cause more of it than any multiway system.

Regards

Charles

[sharpi31]

I see your point now - thanks for the lesson Charles!

My theory would only work if the speed of sound was reduced by the same factor as the difference in size of the mic capsule and drive unit - is this right?

Thanks guys - I'll stumble forwards less ignorant than before :-)

[Hartono]

"My theory would only work if the speed of sound was reduced by the same factor as the difference in size of the mic capsule and drive unit - is this right?"

now this is tooooo much for me to chew

[richie00boy]

You might like to see what Mr Klipsch has to say about it. My website www.readresearch.co.uk in the articles section